| ML 2006
||START Conference Manager
The 2006 ACM SIGPLAN Workshop on ML (ML 2006)
Portland, Oregon, 16th September 2006
Iterating over the elements of an abstract collection is usually done in ML using a fold-like higher-order function provided by the data structure. This article discusses a different paradigm of iteration based on purely functional, immutable cursors. Contrary to fold-like iterators, the iteration can be cleanly interrupted at any step. Contrary to imperative cursors (such as those found in C++ and Java libraries) it is possible to backtrack the iterator to a previous step. Several ways to iterate over binary trees are examined and close links with Gerard Huet's Zipper are established. Incidentally, we show the well-known two-lists implementation of functional queues arising from a Zipper-based breadth-first traversal.